U.S. patent application number 15/503587 was filed with the patent office on 2017-08-17 for method and apparatus for locating of a mobile device.
The applicant listed for this patent is PHILIPS LIGHTING HOLDING B.V.. Invention is credited to JULIUS EVERARDUS PETRUS EBING, ARMAND MICHELMARIE LELKENS, PAULUS MARIA JOHANNES OPPENEER, XIANGYU WANG, HONGMING YANG.
Application Number | 20170234962 15/503587 |
Document ID | / |
Family ID | 51383547 |
Filed Date | 2017-08-17 |
United States Patent
Application |
20170234962 |
Kind Code |
A1 |
YANG; HONGMING ; et
al. |
August 17, 2017 |
METHOD AND APPARATUS FOR LOCATING OF A MOBILE DEVICE
Abstract
As at least part of a location network, there is provided a
trigger node and multiple listening nodes. The trigger node
wirelessly transmits a trigger signal to the mobile device, the
trigger signal being configured to cause the mobile device to
wirelessly emit a signal in response to receiving the trigger
signal. The listening nodes listen for the response signal that was
transmitted from the mobile device in response to the trigger
signal, and thereby at each respective one of a plurality of the
listening nodes that wirelessly receive the response signal from
the mobile device, a respective measurement is taken of the
response signal as received at the respective listening node, for
use in performing a localization to determine the location of the
mobile device based on one or more of these measurements.
Inventors: |
YANG; HONGMING; (EINDHOVEN,
NL) ; LELKENS; ARMAND MICHELMARIE; (HEERLEN, NL)
; EBING; JULIUS EVERARDUS PETRUS; (EINDHOVEN, NL)
; OPPENEER; PAULUS MARIA JOHANNES; (EINDHOVEN, NL)
; WANG; XIANGYU; (EINDHOVEN, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PHILIPS LIGHTING HOLDING B.V. |
EINDHOVEN |
|
NL |
|
|
Family ID: |
51383547 |
Appl. No.: |
15/503587 |
Filed: |
August 11, 2015 |
PCT Filed: |
August 11, 2015 |
PCT NO: |
PCT/EP2015/068460 |
371 Date: |
February 13, 2017 |
Current U.S.
Class: |
342/465 |
Current CPC
Class: |
H04W 64/003 20130101;
G01S 13/74 20130101; G01S 13/878 20130101; G01S 5/04 20130101; G01S
5/14 20130101; G01S 5/0221 20130101; G01S 5/0252 20130101 |
International
Class: |
G01S 5/02 20060101
G01S005/02; G01S 5/14 20060101 G01S005/14; G01S 5/04 20060101
G01S005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 12, 2014 |
EP |
14180653.9 |
Claims
1. A method of determining a location of a mobile device, the
method comprising: as at least part of a location network,
providing a trigger node for transmitting wirelessly to the mobile
device, and providing multiple listening nodes for receiving
wirelessly from the mobile device; using another entity in the
forma presence sensor to detect that a user is within a
predetermined proximity of the presence sensor; using the trigger
node to wirelessly transmit a trigger signal to the mobile device
in response to detecting that the user is within the predetermined
proximity of said presence sensor, the trigger signal being
configured to cause the mobile device to wirelessly emit a signal
in response to receiving the trigger signal; and using the
listening nodes to listen for the response signal that was
transmitted from the mobile device in response to the trigger
signal, and thereby at each respective one of a plurality of the
listening nodes that wirelessly receive the response signal from
the mobile device, taking a respective measurement of the response
signal as received at the respective listening node, for use in
performing a localization to determine the location of the mobile
device based on one or more of said measurements.
2. The method of claim 1, wherein the trigger node is used to
wirelessly transmit the trigger signal periodically at regular
intervals, causing the mobile device to wirelessly emit the
response signal each time it receives the trigger signal.
3. The method of claim 1, wherein the response signal from the
mobile device is a dedicated signal for the purpose of
localization.
4. The method of claim 1, wherein the response signal is emitted
from the mobile device only when triggered by said trigger
signal.
5. The method of claim 1, wherein the response signal from the
mobile device is addressed to a target destination, and the
listening nodes are not the target destination of the response
signal.
6. The method of claim 1, wherein: the trigger node is separate
from the listening nodes, in that the trigger node does not take
any of said measurements of the response signal from the mobile
device, and the listening nodes do not send any trigger signal that
would cause the mobile device to emit the response signal; or the
trigger node also acts as one of the listening nodes, but the rest
of the listening nodes do not send any trigger signal that would
cause the mobile device to emit the response signal.
7. The method of claim 1, wherein the transmission by the trigger
node and the reception by the listening nodes is performed
according to a Wi-Fi protocol, and the trigger signal is an ICMP
message transmitted in response to a ping command.
8. The method of claim 1, wherein the mobile device wirelessly
emits one or more other signals in addition to said response
signal, and each of the listening nodes are used to listen for the
response signal and said other signals even if not addressed to the
listening node, in order to take respective measurements of the
response signal and at least one of the other signals for use in
performing said localization.
9. The method of claim 8, wherein the trigger node is used to
wirelessly transmit the trigger signal to the mobile device in
response to determining that the mobile device has not emitted any
of said other signals within a predetermined time window.
10. Apparatus comprising: a controller configured to use a presence
sensor to detect that a user is within a predetermined proximity of
the presence sensor, and to control a trigger node to wirelessly
transmit a trigger signal to a mobile device in response to
detecting that the user is within the predetermined proximity the
presence sensor, the trigger signal being configured to cause the
mobile device, in response to receiving the trigger signal, to
wirelessly emit a response signal to be received by a plurality of
listening nodes of a location network; and a location engine
configured to receive respective measurements of the response
signal as received at at least some said plurality of listening
nodes, and to perform a localization to determine the location of
the mobile device based on one or more of said measurements.
11. The apparatus of claim 10, wherein the controller is configured
to control the trigger node to wirelessly transmit the trigger
signal periodically at regular intervals, causing the mobile device
to wirelessly emit the response signal each time it receives the
trigger signal.
12. The apparatus of claim 10, wherein: the mobile device
wirelessly emits one or more other signals in addition to the
response signal; each of the listening nodes listen for the
response signal and said other signals even if not addresses to the
listening node, in order to take respective measurements of the
response signal and at least one of the other signals for use in
performing said localization; and the controller is configured to
control the trigger node to wirelessly transmit the trigger signal
to the mobile device in response to determining that the mobile
device has not emitted any of said other signals within a
predetermined time window.
13. A location network for determining a location of a mobile
device, the location network comprising: a presence sensor
configured to detect that a user is within a predetermined
proximity of the presence sensor; a trigger node configured to
wirelessly transmit a trigger signal to the mobile device in
response to detecting that the user is within the predetermined
proximity of said presence sensor, the trigger signal being
configured to cause the mobile device to wirelessly emit a response
signal in response to receiving the trigger signal; and multiple
listening nodes configured to listen for the response signal being
transmitted from the mobile device in response to the trigger
signal, and at each respective one of a plurality of the listening
nodes that wirelessly receive the response signal from the mobile
device, to thereby take a respective measurement of the response
signal as received at the respective listening node; and a location
engine configured to perform a localization to determine the
location of the mobile device based on one or more of said
measurements.
14. A computer program stored on one or more computer-readable
storage media and/or downloadable from a computer network, and
configured so as when executed on one or more processors to perform
an operation of: using a presence sensor to detect that a user is
within a predetermined proximity of the presence sensor;
controlling a trigger node to wirelessly transmit a trigger signal
to the mobile device in response to detecting that the user is
within the predetermined proximity of said presence sensor, the
trigger signal being configured to cause the mobile device, in
response to receiving the trigger signal, to wirelessly emit a
response signal to be received by a plurality of listening nodes of
a location network; and a location engine configured to receive
respective measurements of the response signal as received at at
least some said plurality of listening nodes, and to perform a
localization to determine the location of the mobile device based
on one or more of said measurements.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to localization, i.e. the
process of determining the location of a mobile device based on a
network of wireless nodes.
BACKGROUND
[0002] In an indoor positioning system, the location of a wireless
device such as a mobile user terminal can be determined with
respect to a location network comprising a plurality of wireless
reference nodes, sometimes also referred to as anchor nodes. These
anchors are wireless nodes whose locations are known a priori,
typically being recorded in a location database which can be
queried to look up the location of a node. The anchor nodes thus
act as reference nodes for localization. Measurements are taken of
the signals transmitted between the mobile device and a plurality
of anchor nodes, for instance the RSSI (receiver signal strength
indicator), ToA (time of arrival) and/or AoA (angle of arrival) of
the respective signal. Given such a measurement from three or more
nodes, the location of the mobile terminal may then be determined
relative to the location network using techniques such as
trilateration, multilateration or triangulation. Given the relative
location of the mobile terminal and the known locations of the
anchor nodes, this in turn allows the location of the mobile device
to be determined in more absolute terms, e.g. relative to the globe
or a map or floorplan.
[0003] Another localization technique is to determine the location
of mobile device based on a "fingerprint" of a known environment.
The fingerprint comprises a set of data points each corresponding
to a respective one of a plurality of locations throughout the
environment in question. Each data point is generated during a
training phase by placing a wireless device at the respective
location, taking a measurement of the signals received from or by
any reference nodes within range at the respective location (e.g. a
measure of signal strength such as RSSI), and storing these
measurements in a location server along with the coordinates of the
respective location. The data point is stored along with other such
data points in order to build up a fingerprint of the signal
measurements as experienced at various locations within the
environment. Once deployed, the signal measurements stored in the
fingerprint can then be compared with signal measurements currently
experienced by a mobile device whose location is desired to be
known, in order to estimate the location of the mobile device
relative to the corresponding coordinates of the points in the
fingerprint. For example this may be done by approximating that the
device is located at the coordinates of the data point having the
closest matching signal measurements, or by interpolating between
the coordinates of a subset of the data points having signal
measurements most closely matching those currently experienced by
the device. The fingerprint can be pre-trained in a dedicated
training phase before the fingerprint is deployed by systematically
placing a test device at various different locations in the
environment. Alternatively or additionally, the fingerprint can
built up dynamically by receiving submissions of signal
measurements experienced by the actual devices of actual users in
an ongoing training phase.
[0004] As well as indoor positioning, other types of positioning
system are also known, such as GPS or other satellite-based
positioning systems in which a network of satellites acts as the
reference nodes. Given signal measurements from a plurality of
satellites and knowledge of those satellites' positions, the
location of the mobile device may be determined based on similar
principles.
[0005] The determination of the mobile device's location may be
performed according to a "device-centric" approach or a
"network-centric" approach. According to a device centric approach,
each anchor or reference node emits a respective signal which may
be referred to as a beacon or beaconing signal. The mobile device
takes measurements of signals it receives from the anchor nodes,
obtains the locations of those nodes from the location server, and
performs the calculation to determine its own location at the
mobile device itself. According to a network-centric approach on
the other hand, the anchor nodes are used to take measurements of
signals received from the mobile device, and an element of the
network such as the location server performs the calculation to
determine the mobile device's location. Hybrid or "assisted"
approaches are also possible, e.g. where the mobile device takes
the raw measurements but forwards them to the location server to
calculate its location.
[0006] There are various reasons why it may be desirable to be able
to detect the location of a wireless device, such as to provide
location based services. For instance, one application of a
positioning system is to automatically provide a wireless mobile
device with access to control of a utility such as a lighting
system, on condition that the mobile device is found to be located
in a particular spatial region or zone associated with the lighting
or other utility. E.g. access to control of the lighting in a room
may be provided to a wireless user device on condition that the
device is found to be located within that room and requests access.
Once a wireless user device has been located and determined to be
within a valid region, control access is provided to that device
via a lighting control network. Other examples of location based
services or functionality include indoor navigation, location-based
advertising, service alerts or provision of other location-related
information, user tracking, asset tracking, or taking payment of
road tolls or other location dependent payments. E.g. if a smart
phone can be located in a shop environment, interesting
advertisements can be sent to the mobile phone depending on its
location.
SUMMARY
[0007] The performance of localization technologies, in terms of
accuracy and delay, is often limited due to a small number of
anchor nodes being available and/or limited traffic between the
mobile device and the anchor nodes.
[0008] For instance, one limiting factor for the performance of
such technologies can be the fact that the RSSIs are of a random
nature due to the radio propagation properties. Hence, the accuracy
of such systems can sometimes be limited when there is only a small
number of RSSI measurements available. Hence, it may be desirable
to collect more RSSIs to achieve higher accuracy. Conventionally,
to collect RSSIs, there has to be a direct radio communication
packet exchange between the mobile device and each of the anchor
nodes. This means that in the case where we want to collect a lot
of RSSIs in a system with a large number of anchor nodes, there
would be a lot of data traffic flooding the communication
channel.
[0009] Another potential limiting factor can be the number of
anchor nodes. Many existing solutions use a small number of anchor
nodes. For instance, in Wi-Fi based networks, it is common practice
to use access points (APs) as the anchor nodes. The APs are natural
choices of anchor nodes, since they typically have fixed and known
locations and most of the data traffic goes through an AP
especially in the infrastructure mode. However, the density of AP
deployment is typically quite low. A mobile device can normally set
up a link with only a few APs in practice. Hence the positioning
accuracy can often be limited by the small number of anchor nodes
available.
[0010] With advances in wireless radio communications, there are
more-and-more connected systems with an increasing density of
communication nodes that can be used as anchor nodes. E.g. it has
been proposed to exploit a wireless node incorporated into each of
a plurality of luminaires of a lighting system, such that each
luminaire also acts as an anchor node for localization. However,
one issue that still remains to be solved is how, in practice, one
can collect a significant number of RSSIs from the dense anchor
nodes, preferably without flooding the network with an undue amount
of traffic.
[0011] Thus the performance of location systems such as indoor
location networks often suffers from the lack of sufficient
capturing of RSSI data (or other such signal measurements) from
sufficient number of anchor nodes. It would be desirable to provide
a solution to such issues.
[0012] According to one aspect disclosed herein there is taught a
method in which, as at least part of a location network, there is
provided a trigger node for transmitting wirelessly to the mobile
device, and multiple listening nodes (i.e. receiving anchor nodes)
for receiving wirelessly from the mobile device. The method
comprises: using the trigger node to wirelessly transmit a trigger
signal to the mobile device, the trigger signal being configured to
cause the mobile device to wirelessly emit a response signal in
response to receiving the trigger signal; and using the listening
nodes to listen for the response signal that was transmitted from
the mobile device in response to the trigger signal. At each
respective one of a plurality of the listening nodes that
wirelessly receive the response signal from the mobile device, a
respective measurement is taken of the response signal as received
at the respective listening node. A localization can then be
performed to determine the location of the mobile device based on
one or more of said measurements.
[0013] As the signal emitted from the mobile device is not just
left to chance, but rather explicitly triggered by a signal from
the trigger node, then it can be ensured that at least a certain
desired number of instances of the emitted signal is made available
for use in the localization.
[0014] In embodiments, said response signal is not emitted from the
mobile device except when triggered by said trigger signal. I.e.
the mobile device only emits the response signal in response to
receiving the trigger signal from the trigger node. This can help
prevent the network being flooded with too many signals.
[0015] Another consideration recognised herein, which affects
performance characteristics of positioning systems such as indoor
positioning systems, is that one could achieve smoother positioning
results if the RSSIs or other such measurements were collected more
evenly over time, rather than in a pattern of bursts. E.g. if the
collection of RSSI is dependent on the communication traffic
initiated from the mobile device, such as a mobile phone, the
traffic will hardly be distributed evenly over time. Thus it would
be desirable to be able to collect RSSIs at regular intervals,
rather than in a burst fashion or dependent on the real traffic of
communication nodes.
[0016] Hence in embodiments, the trigger node transmits the trigger
signal periodically at regular intervals, causing the mobile device
to wirelessly emit the response signal each time it receives the
trigger signal (and therefore also periodically).
[0017] In embodiments, the response signal from the mobile device
may be addressed to a target destination (e.g. the trigger node),
and the listening nodes are not the target destination of the
response signal. I.e. the listening nodes "sniff" for the response
signal even though it is not addressed to them.
[0018] In embodiments, the listening nodes are not access points.
E.g. each of the listening nodes may be incorporated into a
respective luminaire.
[0019] In embodiments, the triggered response signal may be a
dedicated signal for the purpose of localization. Nonetheless, it
may also be desirable to further increase the number of signal
measurements available for localization by arranging all listening
anchor nodes to capture ("sniff") all signals (e.g. all packets)
emitted from the mobile device, whether dedicated localization
signals or other signals such as user traffic.
[0020] In yet further embodiments, the mobile device may wirelessly
emit one or more other signals in addition to said response signal;
and each of the listening nodes may listen for the response signal
and said other signals even if not addresses to the listening node,
in order to take respective measurements of the response signal and
at least one of the other signals for use in performing said
localization. In this case, in one particularly advantageous
embodiment, the trigger node may wirelessly transmit the trigger
signal to the mobile device in response to determining that the
mobile device has not emitted any of said other signals within a
predetermined time window (and preferably only in response to
this).
[0021] In embodiments, a proximity of the mobile device to another
entity may be detected and the trigger node may wirelessly transmit
the trigger signal to the mobile device in response to detecting
that the mobile device is within a predetermined proximity of the
other entity.
[0022] In embodiments, the trigger node may be used to detect a
proximity of a user of the mobile device and/or the mobile device
to another entity and wirelessly transmit the trigger signal to the
mobile device in response to detecting that the user and/or mobile
device is within a predetermined proximity of the other entity.
According to another aspect disclosed herein, there is provided
apparatus comprising: a controller configured to control a trigger
node to wirelessly transmit a trigger signal to a mobile device,
the trigger signal being configured to cause the mobile device, in
response to receiving the trigger signal, to wirelessly emit a
response signal to be received by a plurality of listening nodes of
a location network; and a location engine configured to receive
respective measurements of the response signal as received at at
least some said plurality of listening nodes, and to perform a
localization to determine the location of the mobile device based
on one or more of said measurements.
[0023] According to another aspect disclosed herein, there is
provided a location network for determining a location of a mobile
device, the location network comprising: a trigger node configured
to wirelessly transmit a trigger signal to the mobile device, the
trigger signal being configured to cause the mobile device to
wirelessly emit a response signal in response to receiving the
trigger signal; and multiple listening nodes configured to listen
for the response signal being transmitted from the mobile device in
response to the trigger signal, and at each respective one of a
plurality of the listening nodes that wirelessly receive the
response signal from the mobile device, to thereby take a
respective measurement of the response signal as received at the
respective listening node; and a location engine configured to
perform a localization to determine the location of the mobile
device based on one or more of said measurements.
[0024] According to another aspect disclosed herein, there is
provided a computer program stored on one or more computer-readable
storage media and/or downloadable from a computer network, and
configured so as when executed on one or more processors to perform
an operation of: controlling a trigger node to wirelessly transmit
a trigger signal to a mobile device, the trigger signal being
configured to cause the mobile device, in response to receiving the
trigger signal, to wirelessly emit a response signal to be received
by a plurality of listening nodes of a location network; and a
location engine configured to receive respective measurements of
the response signal as received at at least some said plurality of
listening nodes, and to perform a localization to determine the
location of the mobile device based on one or more of said
measurements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] To assist the understanding of the present disclosure and to
show how embodiments may be put into effect, reference is made by
way of example to the accompanying drawings in which:
[0026] FIG. 1 is a schematic representation of an environment
comprising an indoor positioning system,
[0027] FIG. 2 is a schematic block diagram of a system for
providing a location based service,
[0028] FIG. 3 is another schematic representation of an environment
comprising another indoor positioning system,
[0029] FIG. 4 is a schematic block diagram of a message format,
and
[0030] FIG. 5 is a schematic bock diagram of a positioning
system.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0031] FIG. 1 illustrates an example of a positioning system
installed in an environment 2 according to embodiments of the
present disclosure. The environment 2 may comprise an indoor space
comprising one or more rooms, corridors or halls, e.g. of a home,
office, shop floor, mall, restaurant, bar, warehouse, airport,
station or the like; or an outdoor space such as a garden, park,
street, or stadium; or a covered space such as a gazebo, pagoda or
marquee; or any other type of enclosed, open or partially enclosed
space such as the interior of a vehicle. By way of illustration, in
the example of FIG. 1 the environment 2 in question comprises an
interior space of a building.
[0032] The positioning system comprises a location network 4,
comprising multiple reference nodes in the form of anchor nodes 6
each installed at a different respective fixed location within the
environment 2 where the positioning system is to operate. For the
sake of illustration FIG. 1 only shows the anchor nodes 6 within a
given room, but it will be appreciated that the network 4 may for
example extend further throughout a building or complex, or across
multiple buildings or complexes. In embodiments the positioning
system is an indoor positioning system comprising at least some
anchor nodes 6 situated indoors (within one or more buildings), and
in embodiments this may be a purely indoor positioning system in
which the anchor nodes 6 are only situated indoors. Though in other
embodiments it is not excluded that the network 4 extends indoors
and/or outdoors, e.g. also including anchor nodes 6 situated across
an outdoor space such as a campus, street or plaza covering the
spaces between buildings.
[0033] In yet further embodiments the reference nodes 6 need not
necessarily be installed at fixed locations or be dedicated anchor
nodes of an indoor positioning system, as long as their locations
can still be known. For example the reference nodes could instead
be access points 12 of a WLAN or base stations of a cellular
network used for a secondary purpose of positioning, or could be
other mobile devices that have already been positioned, or even
satellites of a satellite based positioning system. The following
will be described in terms of the reference nodes 6 being anchor
nodes of an indoor positioning system or the like, but it will be
appreciated this is not necessarily the case in all possible
embodiments. Also, while the disclosure is described in terms of
wireless radios, the disclosed techniques may be applied to other
modalities such as visible light, ultrasound or other acoustic
waves, etc.
[0034] The environment 2 is occupied by a user 10 having a wireless
device 8 disposed about his or her person (e.g. carried or in a bag
or pocket). The wireless device 8 may take the form of a mobile
user terminal such as a smart phone or other mobile phone, a
tablet, or a laptop computer. At a given time, the mobile device 8
has a current physical location which may be determined using the
location network 4. In embodiments, it may be assumed that the
location of the mobile device 8 is substantially the same as the
location of the user 10, and in determining the location of the
device 8 it may in fact be the location of the user 10 that is of
interest. Another example would be a mobile tracking device
disposed about a being or object to be tracked, e.g. attached to
the object or placed within it. Examples would be a car or other
vehicle, or a packing crate, box or other container. The following
will be described in terms of a mobile user device but it will be
understood this is not necessarily limiting in all embodiments and
most generally the device 8 may be any wireless device having the
potential to be found at different locations or an as-yet unknown
location to be determined. Further, the location of the mobile
device 8 may be referred to interchangeably with the location of
the associated user 10, being or object about which it is
disposed.
[0035] Referring to FIGS. 1 and 2, the environment 2 optionally
comprises at least one wireless access point, router or gateway 12
or the like, enabling communication with a location server 14
(comprising one or more server units at one or more sites). The one
or more wireless access points 12 are placed such that each of the
anchor nodes 6 is within wireless communication range of at least
one such access point or gateway 12. The following will be
described in terms of one access point 12, but it will be
appreciated that in embodiments the same function may be
implemented using one or more access points, wireless routers
and/or gateways or the like distributed throughout the environment
2, or any other means for communicating with the server 14. The
wireless access point or gateway 12 (or the like) is coupled to the
location server 14, whether via a local connection such as via a
local wired or wireless network, or via a wide area network or
internetwork such as the Internet. The wireless access point or
gateway 12 is configured to operate according to a short-range
radio access technology such as Wi-Fi, Zigbee or Bluetooth, using
which each of the anchor nodes 6 is able to wirelessly communicate
via the wireless access point or gateway 12 and therefore with the
location server 14. Alternatively, the environment 2 need not
necessarily comprise any wireless access point, router or gateway
12 or the like. In this case, the nodes may communicate with each
other and with the location server either directly or via mesh
network, etc. As another alternative, it is not excluded that the
anchor nodes 6 could be provided with a wired connection with the
location server 14, but the following will be described in terms of
a wireless connection via an access point 12 or the like. Some
embodiments below may be described in terms of communication via a
wireless access point or gateway 12, but it will be appreciated
this is not limiting to all possible embodiments.
[0036] The mobile device 8 is also able to communicate via the
wireless access point or gateway 12 (or the like) using the
relevant radio access technology, e.g. Wi-Fi, Zigbee or Bluetooth,
and thereby to communicate with the location server 14.
Alternatively or additionally, the mobile device 8 may be
configured to communicate with the location server 14 via other
means such as a wireless cellular network such as a network
operating in accordance with one or more 3GPP standards.
Furthermore, the mobile device 8 is able to communicate wirelessly
with any of the anchor nodes 6 that happen to be in range. In
embodiments this communication may be implemented via the same
radio access technology as used to communicate with the access
point or gateway 12, e.g. Wi-Fi, Zigbee or Bluetooth, though that
is not necessarily the case in all possible embodiments, e.g. the
transmission between the mobile device 8 and anchor nodes 6 may
alternatively use some dedicated localization radio technology.
[0037] Generally any of the communications described in the
following may be implemented using any of the above options or
others for communicating between the respective entities 6, 8, 12,
14 and for conciseness the various possibilities will not
necessarily be repeated each time.
[0038] The signals between the anchor nodes 6 and the mobile device
8 are the signals whose measurements are used to determine the
location of the mobile device 8. In a device centric approach the
anchor nodes 6 each broadcast a signal and the mobile device 8
listens, detecting one or more of those that are currently found in
range and taking a respective signal measurement of each. The
respective measurement taken of the respective signal from each
detected anchor node 6 may for example comprise a measurement of
signal strength (e.g. RSSI), time of flight (ToF), angle of arrival
(AoA), and/or any other property that varies with distance or
location.
[0039] In a network centric approach, the mobile device 8 emits a
signal and the anchor nodes 6 listen, detecting an instance of the
signal at one or more of those nodes 6 that are currently in range.
The respective measurement taken of each instance of the signal
from the mobile device 8 may comprise a measure of signal strength
(e.g. RSSI) or time of flight (ToF), angle of arrival (AoA), and/or
any other property that varies with distance or location. In an
example of a hybrid approach, the nodes 6 may take the measurements
but then send them to the mobile device 8, or the mobile device 8
may take the measurements but send them to the location server
14.
[0040] Time-of-flight measurements can be obtained by establishing
either a one way transmission delay or a two-way transmission delay
(round trip time, RTT). A measurement of one-way delay can suffice
if all relevant elements in the network have a synchronized clock
or can reference a common clock. In this case the mobile device 8
may initiate the measurement with a single message transmission,
adding a timestamp (time or time+date) of transmission to the
message. If on the other hand the measurement is not based on a
synchronized or common clock, the anchor or reference nodes 6 can
still perform a measurement by bouncing individual messages back
from the mobile device 8 and determining the round-trip
time-of-flight. The latter may involve coordination from the nodes
attempting to measure.
[0041] In the case of signal strength measurements, there are also
different options for implementing these. The determination of
distance from signal strength is based on the diminishment of the
signal strength over space between source and destination, in this
case between the mobile device 8 and anchor or reference node 6.
This may for example be based on a comparison of the received
signal strength with a-prior knowledge of the transmitted signal
strength (i.e. if the nodes 6 or mobile device 8 are known or
assumed to always transmit with a given strength), or with an
indication of the transmitted signal strength embedded in the
signal itself, or with the transmitted signal strength being
communicated to the node 6 or device 8 taking the measurement via
another channel (e.g. via location server 14).
[0042] Any one or a combination of these approaches or others may
be applied in conjunction with the system disclosed herein.
Whatever approach is chosen, once such a signal measurement is
available from or at each of a plurality of the anchor nodes 6, it
is then possible to determine the location of the mobile device 8
relative to the location network 4 using a technique such as
trilateration, multilateration, triangulation and/or a fingerprint
based technique.
[0043] In addition, the "absolute" locations of the anchor nodes 6
(or more generally reference nodes) are known, for example from a
location database maintained by the location server 14, or by the
respective location of each anchor node 6 being stored at the node
itself (e.g. and communicated from each relevant nodes to the
mobile device 8 in a device centric approach). The absolute
location is a physical location of the node in a physical
environment or framework, being known for example in terms of a
geographic location such as the location on a globe or a map, or a
location on a floorplan of a building or complex, or any real-world
frame of reference.
[0044] By combining the relative location of the mobile device 8
with the known locations of the anchor nodes 6 used in the
calculation, it is then possible to determine the "absolute"
location of the mobile device 8. Again the absolute location is a
physical location of the device in a physical environment or
framework, for example a geographic location in terms of the
location on a globe or a map, or a location on a floorplan of a
building or complex, or any more meaningful real-world frame of
reference having a wider meaning than simply knowing the location
relative to the location network 4 alone.
[0045] In embodiments, the absolute location of the nodes 6 may be
stored in a human understandable form and/or the absolute location
of the mobile device 8 may be output in a human understandable
form. For example, this may enable the user 10 to be provided with
a meaningful indication of his or her location, and/or may enable
the administrator of a location-based service to define rules for
granting or prohibiting access to the service or aspects of the
service. Alternatively it is possible for the location of the nodes
6 and/or mobile device 8 to only ever be expressed in
computer-readable form, e.g. to be used internally within the logic
of the location based service.
[0046] In other embodiments it is not excluded that the location is
only ever expressed relative to the location network 4, 6 and not
as a more meaningful "absolute" location. For example if each
anchor node 6 is integrated or co-located with a respective
luminaire and the location is being determined for the purpose of
controlling those luminaires, then in some embodiments it may only
be necessary to determine the user's location relative to the
framework of points defined by the anchor nodes of these luminaires
(though in other similar arrangements it may still be desired to
define lighting control regions relative to the floorplan of a
building or the like).
[0047] In a device centric approach the mobile device 8 looks up
the locations of the relevant nodes 6 by querying the location
server 14 (e.g. via the wireless access point or gateway 12), or
alternatively may receive the respective location along with the
signal from each node 6. The mobile device 8 then performs the
calculation to determine its own location at the device 8 itself
(relative to the location network 4 and/or in absolute terms). In a
network centric approach on the other hand, the nodes 6 submit the
signal measurements they took to the location server 14 (e.g. via
the wireless access point or gateway 12), and the location server
14 performs the calculation of the device's location at the server
14 (again relative to the location network 4 and/or in absolute
terms). In an example of an assisted or hybrid approach, the mobile
device 8 may take the measurements of signals from the nodes 6 but
submit them to the location server 14 in a raw or partially
processed form for the calculation to be performed or completed
there.
[0048] Typically a signal measurement is needed from at least three
reference nodes, though if other information is taken into account
then it is sometimes possible to eliminate impossible or unlikely
solutions based on two nodes. For example, if the location is
assumed to be constrained to a single level (e.g. ground level or a
given floor of a building), the measurement from any one given node
6 defines a circle of points at which the mobile device 8 could be
located. Two nodes give two circles, the intersection of which
gives two possible points at which the mobile device 8 may be
located. Three nodes and three circles are enough to give an
unambiguous solution at the intersection of the three circles
(though more may be used to improve accuracy). However, with only
two nodes, sometimes it may be possible to discount one of those
points as being an unlikely or impossible solution, e.g. being a
point in an area to which the user 10 does not have access or it is
impossible to reach, or a point that is not consistent with a
plotted trajectory (path) of the user 10 (elimination by "dead
reckoning"). Similar comments may be made in relation to
three-dimensional positioning: strictly four nodes defining four
spheres are required to obtain an unambiguous solution, but
sometimes an estimate may be made based on fewer nodes if
additional information can be invoked. Assuming the user 10 is
constrained to a particular level to constrain to a two-dimensional
problem is an example of such information. As another example, it
may be assumed the user 10 is found on one of a plurality of
discrete floors, and/or a dead reckoning type approach may be used
to eliminate unlikely jumps in the user's route.
[0049] By whatever technique the location is determined, this
location may then be used to assess whether the mobile device 8 is
granted access to some location-based service or other such
function. To this end, there is provided a service access system 16
configured to conditionally grant access to the service in
dependence on the absolute location of the mobile device 8. In a
device centric approach the mobile device 8 submits its determined
absolute location (e.g. in terms of global coordinates, map
coordinates or coordinates on a floor plan) to the service access
system 16 over a connection via the wireless access point 12 or
other means such as a cellular connection. The service access
system 16 then assesses this location and grants the mobile device
8 with access to the service on condition that the location is
consistent with provision of the service (and any other access
rules that happens to be implemented, e.g. also verifying the
identity of the user 10). In a network centric approach, the
location server 14 submits the determined absolute location of the
mobile device 8 to the service access system 16, e.g. via a
connection over a local wired or wireless network and/or over a
wide area network or internetwork such as the Internet.
Alternatively the location server 14 may send the absolute location
to the mobile device 8, and the mobile device may then forward it
on to the service access system 16. In another alternative the
service could be provided directly from the location server 14, or
could even be implemented on an application running on the mobile
device 8 itself.
[0050] The following are some examples of location-related services
or functions that may be provided in accordance with embodiments of
the present disclosure: [0051] allowing control of a utility such
as lighting from an application running on the mobile device 8,
where the user can only control the lighting or utility in a given
room or zone when found to be located in that room or zone, or
perhaps an associated zone; [0052] providing a navigation service
such as an indoor navigation service to the mobile device 8 (in
which case the location-related function comprises at least
providing the device's absolute location to an application running
on the mobile device 8, e.g. which the application may then use to
display the user's location on a floor plan or map); [0053]
providing location based advertising, alerts or other information
to the mobile device 8, e.g. providing the device 8 with
information on exhibits as the user 10 walks about a museum,
providing the device 8 with information about products as the user
10 walks about a shop or mall, providing the device 8 with access
to medical data only if present inside a hospital or specific zone
within a hospital, or providing the device 8 with access to
complementary media material only if present physically within a
movie theatre or the like; and/or [0054] accepting location
dependent payments from the mobile device on condition that the
device 8 is present in a certain region, e.g. payments in shops,
payment of road tolls, "pay as you drive" car rental, or entrance
fees to venues or attractions.
[0055] For instance, in embodiments the service access system 16 is
configured to control access to a lighting network installed or
otherwise disposed in the environment 2. In this case the
environment 2 comprises a plurality of luminaires (not shown) and a
lighting control system comprising the access system 16. The
luminaires may for example be installed in the ceiling and/or
walls, and/or may comprise one or more free standing units. The
luminaires are arranged to receive lighting control commands from
the controller. In embodiments this may also be achieved via the
wireless access point 12 using the same radio access technology
that the anchor nodes 6 and/or mobile device 8 use to communicate
with the wireless access point or gateway 12, and/or the same radio
access technology used to communicate the signals between the
mobile device 8 and anchor nodes 6 in order to take the location
measurements, e.g. Wi-Fi or Zigbee. Alternatively the lighting
controller may communicate with the luminaires by other means, e.g.
a separate wired or wireless network. Either way, the access system
16 of the lighting controller is configured with one or more
location dependent control policies. For example, a control policy
may define that a user 10 can only use his or her mobile device 8
to control the lights in certain region such as a room only when
found within that region or within a certain defined nearby region.
As another example control policy, the mobile device 8 only
controls those luminaires within a certain vicinity of the user's
current location.
[0056] With regard to security, provided that the localization
messages are distributed internally within the localization system
4, 6, 14 security may be less of an issue; but in the case of
two-way time of flight messages (RTT) for example, or where the
reports are transmitted over a public network, it may be
advantageous to provide them with a time-stamp (measurement time)
or a nonce and/or to "hash" the messages (digital signature) so as
to thwart any replay attacks on the network backbone. The same
could be done with the measurement reports sent to the location
server 14. Such measures are not essential but may be desirable in
embodiments, particularly if the location-based service or
functionality is susceptible to abuse or involves financial
transactions or the like.
[0057] Note that FIG. 2 shows arrows in all directions to
illustrate the possibility of either device centric or network
centric approaches, but in any given implementation not all the
communications shown need be bidirectional or indeed present at
all. Network centric, device centric and assisted approaches are
described by way of comparison, but the following embodiments will
relate to a network centric approach whereby anchor nodes 6 of the
location network 4 take measurements of signals received from the
mobile device 8 and the location server 14 or other network element
performs the localization calculation based on these measurements,
or a hybrid approach in which the anchor nodes 6 take the
measurements of the signals from the mobile device 8 but return the
measurements to the mobile device 8 for the localization
calculation to be performed there. In both these scenarios, each of
the anchor nodes 6 is acting as a "listening" node which listens
for signals to receive from the mobile device 8. In the following
therefore, the anchor nodes may be referred to as listening nodes,
or "sniffers" (for reasons that will become apparent). The
computing entity performing the localization may be referred to as
the localization engine, which may be implemented in software
and/or hardware whether at the location server 14 or other network
element (network centric approach) or at the mobile device 8
(hybrid approach).
[0058] As mentioned, the performance of location systems such as
indoor location systems often suffers due to a lack of sufficient
capturing of RSSI data (or other such signal measurements) at
sufficient number of anchor nodes 6. It would be desirable to
provide a solution to such issues, but preferably without flooding
the communication network with too many communications.
[0059] The following provides a system and method to enhance the
performance of indoor location networks or other such location
systems, by providing a mechanism for externally controlling the
occurrence of signals from the mobile device for the purpose of
localization, and in embodiments also exploiting the availability
of other traffic already being transmitted by the mobile device 8
for other purposes (such as to communicate user content).
[0060] Referring to FIGS. 3 and 5, the system comprises three
parts. The first part is a trigger node 18. The trigger node 18 is
arranged to send trigger signals to each target mobile device 8,
which react by emitting a signal. The second part consists of a
number of radio receivers, the listening anchor nodes 6, which are
configured as "sniffers". The functionality of each sniffer 6 is to
determine the identification of the mobile device 8 from the
emitted signal and derive the RSSIs at the sniffer 6 (or derive
another such measurement suitable for use in localization--the
following will be described in terms of RSSI but it will be
appreciated this is not limiting). Finally, all the RSSI data are
communicated to an aggregation node 28, which connects to a
location engine 30 to compute the location of each target mobile
device 8. The location engine 30 may be implemented at the location
server 14 (network centric approach) or at the mobile device 8
(hybrid approach), or at the trigger node 18 or another node, or
any combination of these. It may be implemented in software stored
in one or more memories of the server 14, mobile device 8 and/or
other node and arranged for execution on one or more processors of
the server 14, mobile device 8 and/or other node; or may be
implemented in dedicated hardware circuitry, or in configurable or
reconfigurable circuitry such as a PGA or FPGA, or any combination
of these possibilities.
[0061] To elaborate, within the location network 4, as well as the
listening anchor nodes 6 there is also provided a trigger node 18.
The role of the trigger node 18 is to send communication packets to
each mobile device 8, with each packet comprising a trigger message
in order to trigger a wireless response from the target mobile
device 8. The trigger node 18 is configured to transmit the trigger
packets under control of a controller 19, which may for example be
implemented at the trigger node 18 or the location server 14, or
elsewhere. This controller 19 may be implemented in software stored
in one or more memories of the server 14, trigger node 18 and/or
other node and arranged for execution on one or more processors of
the server 14, trigger node 18 and/or other node; or may be
implemented in dedicated hardware circuitry, or in configurable or
reconfigurable circuitry such as a PGA or FPGA, or any combination
of these possibilities.
[0062] Each trigger packet may be broadcast to any devices that are
in range including the target mobile device(s) 8, or alternatively
each trigger packet may be addressed to a specific target mobile
device 8 which the trigger node 8 has detected within the
environment 2. Either way, this triggers a response to be emitted
by the mobile device 8 in order to act like a beacon by which the
location of the mobile device 8 can be detected by the location
network 4. This response by the mobile device 8 may be broadcast or
may be addressed to the trigger node 18. In the latter case, the
response will still be detectable by at least some of the listening
anchor nodes 6 in the environment 2, which in embodiments are
configured to "sniff" for any signals from the mobile device 8 even
if not addressed to them (as will be discussed in more detail
shortly).
[0063] In principle, any communication node in the network could
act as the trigger node 18. For instance, one possible choice for a
WiFi network would be to configure the access point (AP) 12 (or one
of multiple APs) to act as the trigger node 18, since all the data
traffic will pass through the AP anyway in the infrastructure mode.
I.e. in embodiments the trigger node 18 comprises an access point
for providing user devices such as the mobile device 8 with access
to a further, communications network such as the internet via the
same wireless access technology (e.g. Wi-Fi or ZigBee) that is used
to transmit the trigger signal. Note therefore that although
elements 12 and 18 are shown separately in the schematic
illustration of FIG. 3, in embodiments they may in fact be
incorporated in the same unit and represent different functions of
that same node. Alternatively, it is not excluded that the trigger
node 18 could indeed be a separate node, i.e. a node other than the
AP or gateway 12, e.g. a dedicated trigger node introduced solely
for that purpose, or another type of node such as a Wi-Fi, ZigBee
or Bluetooth equipped luminaire.
[0064] In embodiments, the trigger node 18 is configured (under
control of its controller 19) to send the trigger packets at
regular intervals, i.e. periodically, such that all the sniffer
nodes 6 also can obtain RSSIs with a regular interval. Such regular
collection of RSSIs can offer more stable and smooth location
results than based on the traffic of a burst pattern, such as the
natural traffic patterns that are commonly initiated by mobile
devices. Further, in embodiments, the duration of the interval may
be arranged to have a direct correlation with the achievable
positioning performance in terms of accuracy and delay, etc. In
some particularly advantageous embodiments, the duration of the
interval can be adapted based on positioning performance
requirements such as accuracy and/or delay. For instance, in an
emergent situation, a higher accuracy or lower delay is needed than
normal situations to determine the location of a mobile device, and
the transmission interval between the trigger signals is shortened,
so that more RSSI measurements can be obtained within a relatively
shorter time.
[0065] The mobile device 8 comprises a local controller 9 which may
be implemented in software stored in one or more memories of the
mobile device 8 and arranged for execution on one or more
processors of the mobile device, or may be implemented in dedicated
hardware circuitry, or in configurable or reconfigurable circuitry
such as a PGA or FPGA, or any combination of these possibilities.
The controller 9 is configured to recognize the trigger message
sent from the trigger node 18 when received by the mobile device,
and to react accordingly by controlling the mobile device 8 to
wirelessly emit a signal in response whenever the trigger message
is received from the trigger node 18. If the trigger signal is
transmitted regularly, this will cause the mobile device 8 to emit
the response signal in response to each trigger packet and
therefore to respond with the response signal at substantially
regular intervals as well.
[0066] In one example implementation, the trigger message may be
transmitted in the form of an ICMP (Internet Control Message
Protocol) message initiated by a network "ping" command for a Wi-Fi
network, executed at the controller 19 of the trigger node 18. In
this case the response signal from the mobile device 8 takes the
form of a ping response message. However, it will be appreciated
this is just one example, and in other embodiments other use
methods such as TPC request/report can be used.
[0067] In embodiments, the "sniffer" nodes 6 are in fact normal
and/or pre-existing wireless communication client nodes in the
network that are configured with an additional "sniffing"
functionality. According to this functionality, each sniffer node 6
listens to the response messages from the mobile device 8 to the
trigger node 18, and estimates the respective signal strengths
(RSSIs) at the respective sniffer node 6.
[0068] Consider a wirelessly connected system with a lot of nodes 6
in the system. These nodes 6 are deployed around various places in
the environment 2, and are able to communicate wirelessly with each
other via WiFi, ZigBee or the like. For example these nodes 6 could
be wirelessly connected lamps, access points, computers, wireless
speakers, etc. These nodes 6 are of fixed and known locations. Each
of them may have their own pre-existing purpose for being equipped
with their wireless communication capabilities (e.g. Wi-Fi or
ZigBee), such as to allow wireless control of the colour and/or
dimming level of the emitted light in the case where the nodes
comprise lamps. In embodiments, this wireless capability of the
nodes 6 is exploited such that they are also used to act as anchor
nodes for the purpose of localization. However, localization need
not be the primary purpose for which they are equipped with
wireless communication capability (e.g. Wi-Fi or ZigBee) and in
embodiments it is indeed not the primary purpose. Note also that in
embodiments, some or all of the nodes 6 used as anchor nodes are
not access points (APs), i.e. do not provide user devices such as
the mobile device 8 with wireless access to any further
communication network such as the Internet (e.g. instead they are
luminaires with wireless capability). Alternatively it is not
excluded that some or all of these nodes 6 could be access
points.
[0069] Note, the concept of an AP only applies to the example of
Wi-Fi systems. However, the scope of the present disclosure is not
limited to any particular radio technology. More generally, any of
the involved nodes, including the trigger node, the mobile device,
the anchor node, the aggregation node, etc., can be a normal
station, or wireless client node.
[0070] Each communication node 6 has a unique identification (ID),
such as an IP address or MAC address, or the like. A common
practice for each communication node 6 to receive data is as
follows. As illustrated in FIG. 4, typically each transmitted
packet comprises a header 20 and a payload 22. The header 20
comprises a source ID 24 being the ID of the source of the packet
source, and a destination ID 26 being the ID of the destination of
the packet. Each communication node listens to the radio waves in
the environment 2. Once each node receives a packet, it checks
whether the destination ID is the ID of itself. If yes, then the
communication node decodes the rest of the data inside the packet
payload 22. If not, then the node simply discards the packet or
forwards the packets to other nodes, without looking into the rest
the packet.
[0071] In embodiments, the "sniffing" can be implemented in the
listening nodes 6 by changing the normal receiving strategy, as
follows. Once seeing a packet, irrespective of the destination ID,
each listening node 6 checks the source ID in the packet header and
estimates the receive signal strength (e.g. RSSI) based on the
packet header 20 or the entire packet 20, 22, without decoding the
rest of the packet. The rest of the data packet may be encrypted
anyway and not understandable for a node 6, if the destination ID
is not same as that node 6. However, the listening node 6 does not
need to understand the content, but rather only measure the
received signal strength. In this manner, each sniffer node 6
behaves as an anchor node and it can collect the RSSIs with respect
to any mobile device 8 even if there is no direct communication
between the mobile device 8 and the listening node 6 (i.e. even if
the mobile device 8 does not specifically address any communication
to the listening node 6). In this sense, the listening node 6 may
be said to "sniff" for combinations from the mobile device 8, even
if not intended for it.
[0072] N.B. in conventional location systems, the device emits a
beacon signal which is broadcast, i.e. not addressed to any
specific destination. However, in embodiments of the present
disclosure, the response signal from the mobile device may not be a
broadcast signal, but rather is addressed to a specific
destination, e.g. the trigger node--but nonetheless, the anchor
nodes 6 (referenced nodes) are configured to listen for the signal
anyway even though not addressed to them. Therefore, the word
"sniffer" may be used herein to refer to the reference nodes.
[0073] The RSSIs from various different sniffer nodes 6 are sent by
the respective sniffer nodes 6 to an aggregation node 28. The role
of the aggregation node 28 is to collect all the RSSIs from all the
sniffer nodes 6 that detect a signal from the mobile device, and to
send them to the location engine 30 to actually compute the
locations of the mobile device (s) 8. The aggregation node 28 may
be any suitable node of the network, whether a dedicated
aggregation node introduced for that purpose, or one of the other
nodes already described such as an access point 12 or the trigger
node 18 or other some other node (thus although labelled and/or
shown separately in the schematic illustrations of FIGS. 3 and 5,
in embodiments elements 28 and 12 and/or 18 may represent different
functions incorporated in the same unit).
[0074] Various different location algorithms can be used at the
location engine 30, such as trilateration, fingerprinting, or radio
zoning, etc.; based on any suitable measurements such as RSSI or
time-of-flight. Note also, the localization need only be based on
at least some of the measurements from nodes that hear the response
(i.e. it doesn't necessarily have to use all available
measurements).
[0075] In embodiments, the trigger node 18 and the listening
(sniffer) anchor nodes 6 are distinct types of node. The trigger
node 18 may be separate from the listening nodes 6, in that the
trigger node 18 does not take any of said measurements of the
triggered response signal from the mobile device 8, and the
listening nodes 6 do not send any trigger signal that would cause
the mobile device 8 to emit the response signal; or the trigger
node 18 may also acts as one of the listening nodes 6, but the rest
of the listening nodes 6 do not send any trigger signal that would
cause the mobile device 8 to emit the response signal.
[0076] The system diagram is illustrated in FIG. 5, where
solid-line connections indicate a "real" target communication link
(to an addressed destination) while dashed lines indicate a
sniffing communication link (not to the addressed destination).
[0077] In embodiments, the signal emitted by the mobile device 8 in
response to the trigger is a dedicated signal for the purpose of
localization, i.e. it does not contain any user content, nor any
control information other than for the purpose of localization.
[0078] Preferably, the mobile device 8 is configured (under control
of its controller 9), so that it will only transmit the response
signal in response to receiving the trigger signal from the trigger
node 18, and not otherwise. This way the external control of the
emissions triggered by the trigger node 18 can not only ensure
there are sufficient messages for location, but also that there are
not too many messages being transmitted which could otherwise cause
congestion over the wireless network.
[0079] Note also that in embodiments, the sniffer nodes 6 are not
limited to only detecting and taking measurements of the response
signal sent from the mobile device 8 in response to the trigger
signal from the trigger node 18. Rather, the mobile device 8 may
transmit other traffic in the form of user content and/or control
signals transmitted for purposes other than localization (which
traffic does not have to wait to be triggered by the trigger
signal); and the sniffer nodes 6 are preferably configured to
detect and take measurements of any signal from the mobile device 8
including such other non-localization traffic, and to report these
to the location engine 30 (via aggregation node 28) to be included
in the localization calculation. I.e., the signal measurements for
use in the localization are taken from both natural traffic and
triggered traffic.
[0080] In further embodiments, the system may be arranged to
implement a degree of cooperation between the trigger node 18 and
sniffer nodes 6. In this case, the sniffer nodes 6 are arranged to
receive an indication from the controller 19 of the trigger node 18
indicating when the trigger signal has been sent to the mobile
device 8. Based on this, the sniffer nodes 6 are configured so that
they only "sniff" for messages within a short time window soon
after a trigger message is sent by the trigger node 18. For the
rest of time, the sniffing nodes are configured to switch off to a
power-save mode. This provides an intelligent search strategy by
which only devices 8 that didn't recently communicate are
triggered. Thus by cooperating between the trigger node 18 and
sniffer nodes 6, additional power saving can be achieved.
[0081] In yet further embodiments, the system is arranged to detect
a proximity of the mobile device 8 to some other entity, and the
trigger node 18 is configured (under control of its controller 19)
to wirelessly transmits said trigger signal to the mobile device in
response to detecting that the mobile device 8 is within a
predetermined proximity of the other entity (and in embodiments
only in response to this). For example the other entity could be a
presence sensor (not shown) such as an infrared sensor or
ultrasound sensor for detecting that the user 10 is proximate to
the sensor, with the presence sensor being located near the trigger
node 18 or at a central or otherwise representative location
amongst the sniffer nodes 6 such that proximity to the presence
sensor indicates the mobile device 8 is in a suitable place for a
localization to be performed based on the sniffer nodes 6 in the
environment 2 in question. As another example, the location engine
30 may be configured to obtain an initial, rough location based on
previous measurements, perhaps including extrapolating the path of
the mobile device from base localizations, and this may be used to
determine proximity between the mobile device 8 and the trigger
node 18 or one or more of the sniffer nodes 6. By whatever means
the proximity detection is achieved, when the mobile device 8 is
known to be proximate to the other "landmark" entity, then the
trigger node 8 starts measurements by triggering devices 8 in
proximity to the landmark entity. This may be performed in a manner
so as to allow fast triangulation, trilateration or the like--e.g.
once RSSI data from two sniffer nodes 6 are known, the location
engine 30 picks a third based on known topology and RSSI1 and
RSSI2.
[0082] It will be appreciated that the above embodiments have been
described only by way of example.
[0083] In accordance with everything discussed above, the
techniques disclosed herein advantageously introduce a trigger node
into a wireless network in order to aid localization. Various
concepts have been disclosed, including: (i) nodes in the network,
look at communications in the network (also those not intended for
them) to determine RSSI measurements to other nodes, and these RSSI
values are combined to determine relative position; (ii) a trigger
node sends trigger messages to other nodes to trigger responses
(the trigger also performs RSSI measurement) and determines RSSI to
other nodes; and (iii) both can be advantageously combined because
then you can "tune" the messages of the trigger device to only
trigger responses from devices that are e.g. not active. In
embodiments technique (i) can be used alone, or even more
advantageously in combination with (ii) or (ii) and (iii).
[0084] Further, note that although the above has been disclosed in
terms of certain wireless communications standards such as Wi-Fi
and ZigBee, these are not limiting and the localization techniques
disclosed herein can be implemented using any wireless standard or
proprietary wireless protocol. Further, the scope of the disclosure
is not limited to any one particular type of localization
calculation, and various examples will in themselves be appreciated
by a person skilled in the art, e.g. triangulation, trilateration,
multilateration, or fingerprinting. Nor is the scope of the
disclosure limited to using RSSI or other measure of received
signal strength as the measurements for performing localization,
and other types of measurement are possible, such as
time-of-flight.
[0085] Other variations to the disclosed embodiments can be
understood and effected by those skilled in the art in practicing
the claimed invention, from a study of the drawings, the
disclosure, and the appended claims. In the claims, the word
"comprising" does not exclude other elements or steps, and the
indefinite article "a" or "an" does not exclude a plurality. A
single processor or other unit may fulfil the functions of several
items recited in the claims. The mere fact that certain measures
are recited in mutually different dependent claims does not
indicate that a combination of these measures cannot be used to
advantage. A computer program may be stored/distributed on a
suitable medium, such as an optical storage medium or a solid-state
medium supplied together with or as part of other hardware, but may
also be distributed in other forms, such as via the Internet or
other wired or wireless telecommunication systems. Any reference
signs in the claims should not be construed as limiting the
scope.
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